A spring fire that killed an elderly couple raced across the dry foothills southwest of Denver, prompting officials to alert residents to be ready to evacuate. Officials said the fire had consumed at least 4,500 acres and burned 23 structures, The Denver Post reported Wednesday. An elderly couple died on their property in the Lower North Fork fire and crews were searching late Tuesday for a woman missing in the fire area. Authorities alerted residents Tuesday afternoon that an additional 6,500 homes should prepare to evacuate after a fire flared a mile northwest of Waterton Canyon. About 2,500 homes have already been evacuated, the Post said. Despite the work by some 200 firefighters, authorities failed to gain much control over the fast-moving fire, Jacki Kelley, a Jefferson County Sheriff\'s Office spokeswoman, said. The firefighting team was expected to increase to 400 Wednesday, with crews coming in from across the western United States, Kelly said. \"We\'re finally getting the resources we needed yesterday,\" Kelley said. \"We\'re going to be fighting this fire 24 hours a day until we get containment.\" The fire, fanned by high winds and fueled by dry conditions, moved across thousands of acres southwest of Denver starting Monday. Jefferson County officials said they think the fire began as a controlled burn set a week ago by the Colorado State Forest Service that reignited. However, Joe Duna, a deputy state forester, told a Denver television station the service questioned the source of the blaze that started so long after the controlled burn. \"I think it\'s fairly unusual for this to happen so long after the fact, and so we\'ll wait for the sheriff\'s report,\" Duna said.